Semiconductor devices have been highly integrated and advanced in processing speed by shifting the wavelength of a light source shorter to attain a finer pattern size in lithography technologies using a light exposure (photolithography) as common arts. In order to form such a fine circuit pattern on a semiconductor device substrate (a substrate to be processed), the substrate is usually processed by dry etching using a photoresist film having a formed pattern as an etching mask. Practically, however, there is no dry etching method having a complete etching selectivity between the photoresist film and the substrate to be processed. Accordingly, substrate processing by a multilayer resist process has been commonly used recently. In this method, a middle layer film having a different etching selectivity from a photoresist film (hereinafter, a resist upper layer film) is set between the resist upper layer film and a substrate to be processed, and a pattern is obtained on the resist upper layer film, and subsequently the pattern is transferred to the middle layer film by dry etching using the resist upper layer film pattern as a dry etching mask, and the pattern is further transferred to the substrate to be processed by dry etching using the middle layer film as a dry etching mask.
One of the multilayer resist processes is a three-layer resist process, which can be performed by using a conventional resist composition that is used in a single layer resist process. In this process, an organic under layer film material composed of a composition containing an organic resin is applied onto a substrate to be processed and is baked to form an organic under layer film (hereinafter, an organic film), a resist middle layer film material composed of a silicon-containing resin composition is applied thereto and is baked to form a silicon-containing film (hereinafter, a silicon middle layer film), and a conventional resist upper layer is formed thereon. After patterning the resist upper layer film, the resist upper layer film pattern can be transferred to the silicon middle layer film by dry etching with a fluorine-base gas plasma since organic resist upper layer films have excellent etching selectivity to silicon middle layer films. This method makes it possible to easily transfer a pattern to a silicon middle layer film even in the use of a resist upper layer film without having a sufficient film thickness for directly processing a substrate to be processed or a resist upper layer film without having a sufficient dry etching durability for processing a substrate to be processed since the silicon middle layer film usually has a film thickness equal to or less than that of the resist upper layer film. The pattern can be transferred to the organic under layer film that has sufficient dry etching durability for substrate processing by transferring the pattern to the organic under layer film by dry etching with an oxygen base or hydrogen base gas plasma using the silicon middle layer film having the pattern transferred thereon as a dry etching mask. This organic under layer film pattern having the pattern transferred thereon can be transferred to a substrate by dry etching by using a fluorine base gas or a chlorine base gas.
On the other hand, the attempt to produce smaller pattern sizes in production processes of semiconductor devices is approaching the inherent limit due to the wavelength of a light source for photolithography. Accordingly, higher integration of semiconductor devices have been investigated recently without depending on smaller pattern sizes. In one of these methods, semiconductor devices with complicated structures have been investigated including a multi gate structure and a gate all-around, and a part of them have been put to practical use already. When these structures are formed by a multilayer resist process, it is possible to apply an organic film material that is capable of planarization by gap filling a minute pattern formed on a substrate to be processed such as a hole, a trench, and a fin with the organic film material without a void, or planarization by filling a step or a pattern dense portion and no pattern region with the organic film material. Such an organic film material is used for forming a planar organic under layer film surface on a stepped substrate to decrease fluctuation of a film thickness of a silicon middle layer film or a resist upper layer film formed thereon, thereby making it possible to avoid the deterioration of depth of focus in photolithography or a margin in the subsequent processing step of a substrate to be processed. This makes it possible to produce semiconductor devices in good yield. On the other hand, it is difficult to produce semiconductor devices in a good yield by a single layer resist process since it requires an upper layer resist film to have thicker film thickness for gap filling a stepped or patterned substrate to be processed, thereby causing lower tolerance for pattern forming in exposure such as pattern collapse after exposure and development as well as degradation of a pattern profile due to reflection from a substrate in exposure.
As a method for next-generation semiconductor devices to achieve higher processing speed, investigations have been undertaken on new materials that have high electron mobility using strained silicon and gallium-arsenic etc. or fine materials such as an ultrathin film polysilicon whose thickness is controlled at the angstrom level. When such a new fine material is applied to a substrate to be processed, however, the material can be corroded with oxygen in air atmosphere under conditions in forming a planar film using the organic under layer film material as described above, for example, the film forming conditions of 300° C. or more in air atmosphere. This risks the semiconductor device to fail to attain higher processing speed as it is designed, and fail to attain the yield that can be managed as industrial manufacturing. Accordingly, an organic under layer material that can be formed in an inert gas is demanded in order to avoid lowering of the yield due to corrosion of a substrate with air atmosphere under the higher temperature conditions.
As a material for forming an organic film for a multilayer resist process, condensation resins have been known including a phenolic or naphtholic compound using a carbonyl compound such as ketones and aldehydes or aromatic alcohols as a condensation agent. Illustrative examples thereof include fluorene bisphenol novolak resins described in Patent Literature 1, bisphenol compounds and novolak resins thereof described in Patent Literature 2, novolak resins of adamantanephenol compounds described in Patent Literature 3, and bisnaphthol compounds and novolak resins thereof described in Patent Literature 4. These materials are formed into a film that has solvent resistance to the coating film material used in the subsequent step by crosslinking thereof with a methylol compound as a crosslinking agent or curing function due to crosslinking reaction including oxidation of the aromatic ring at the α-position by an effect of oxygen in air atmosphere, followed by condensation.
Additionally, Patent Literatures 5 to 10 have been known as examples of each material in which a triple bond is used as a group for intermolecular crosslinking of a curable resin. For these materials, however, the actual curing conditions in an inert gas is not exemplified. There is no information on forming the cured film of these materials in an inert gas or fluctuation of film thicknesses due to thermal decomposition under high temperature conditions.